Morphogenesis during molting of the setae in the statocyst sensilla of the mysid shrimp Neomysis integer (Leach, 1814) (crustacea,mysidacea)

The morphogenesis of the setae in the statocyst sensilla of Neomysis integer was studied. Immediately before ecdysis, a new seta lies inverted between the enveloping cells. All of the nine enveloping cells, except the first one, secrete a well defined part of the new seta. The second, third, fourth, and fifth have a trichogen function; the sixth has a trichogen-tormogen function; and the seventh, eighth, and ninth enveloping cells have a tormogen function. It could not be established whether the dendritic sheath is replaced at molt. In the second and third enveloping cells, there is a differential secretion of cuticular material forming the wall of the distal part of the seta. As a consequence, this wall is not homogeneous. The possible role of this heterogeneity in the formation of the gutter-like apical part of the seta is discussed. A mechanism is proposed by which the pore develops at the transition between the midpart and the apical gutter-like part. Before ecdysis, the distal segments of the sensory cells are still connected with the wall of the old seta in the same way as during intermolt. No degeneration is apparent in the distal segments during preparation for the molt. These morphological findings suggest that sensitivity of the sensilla must be maintained until the moment of the ecdysis.     

Fine structure and ecdysis of mandibular sensilla associated with the lacinia mobilis in Neomysis integer (Leach, 1814) (Crustacea,Malacostraca, Peracarida)

The external and internal structures of adult Neomysis integer mandibles were studied using light and electron microscopy with special reference to the lacinia mobilis, a highly specialized appendage on the gnathal edge of many crustaceans. The right and left lacinia mobilis are equipped with ciliary primary sensory cells revealing that both laciniae are also mechanosensory organs in addition to their mechanical function during mastication. A detailed character analyses indicated that the right lacinia is probably a highly derived sensory seta, whereas two alternative interpretations are considered for the left lacinia; it could be a sensillar appendage equipped with two mechanosensory units, or it could be a movable appendage of the incisor process containing two sensilla deprived of external appendages. The ecdysis of the lacinia mobilis corresponds very well to type I sensillar ecdysis, suggesting classification as a sensillar appendage. These features support a possible homology of the right lacinia mobilis in Peracarida and Decapoda, tracing them to an origin as a member of the setal row. Whether the left lacinia mobilis is a sensillum or an appendage with sensilla cannot be resolved presently.     

Development of antennal sensilla during moulting inNeomysis integer (Leach) (Crustacea,Mysidacea)

Summary The sensilla are associated with 6 enveloping cells. The innermost enveloping cell (e 1) secretes the dendritic sheath (=thecogen cell). All other enveloping cells are involved in the formation of the outer cuticular apparatus in secreting the cuticle of a definite region of the new hair shaft.The development of the new sensilla begins when an exuvial space expands between old cuticle and epithelium. The newly forming hair shafts lie folded back in an invagination of the epidermal tissue. Only a distal shaft part projects into the free exuvial space. The cuticle of the distal and middle shaft region is secreted by the three middle enveloping cells (e 2–e 4) (=trichogen cells), which are arranged around the dendritic sheath.The wall of the cylinder, in which the distal shaft is situated, is formed by the cuticle of the future proximal shaft region. It is secreted by the outer enveloping cells (e 5 and e 6). Furthermore, both enveloping cells form the hair socket (=trichogen-tormogen cells).The outer dendritic segments encased within a dendritic sheath run up through the newly formed hair shaft and continue to the old cuticular apparatus. The connection between sensory cells and old hair shaft is maintained until ecdysis. On ecdysis the old cuticle is shed and the newly formed shaft of the sensillum is everted like the invaginated finger of a glove. The dendritic sheath and the outer dendritic segments break off at the tip of the new hair shaft. Morphologically this moulting process ensures that the sensitivity of the receptors is maintained until ecdysis.The internal organization of the sensory cells shows no striking changes during the moulting cycle. An increased number of vesicles is accumulated distally within the inner dendritic segments and distributed throughout the outer segments of the dendrites. The cytoplasmic feature of the enveloping cells indicates that synthesis and release of substances for the cuticular apparatus of the new sensillum take place.     

Purification and characterization of vitellin from the estuarine mysid Neomysis integer (Crustacea; Mysidacea)

Invertebrates account for roughly 95% of all animals, yet surprisingly, little effort has been invested to understand their value in signaling potential environmental endocrine disruption. There has been, however, much recent attention on vitellogenin induction in egg-laying invertebrates and vertebrates as indicators of exposure to estrogenic xenobiotics. Mysid shrimp (Crustacea: Mysidacea) have been put forward by several researchers and regulatory bodies (e.g., US-EPA) as suitable test organisms for the evaluation of environmental endocrine disruption. In view of developing sensitive assays to study endocrine disruption in the estuarine mysid Neomysis integer, we isolated and characterized vitellin, the major yolk protein in eggs. Vitellin was purified using gel filtration and characterized by electrophoresis using different staining procedures. Specific (as shown by Western blotting) polyclonal antibodies were produced in rabbit against the purified vitellin of N. integer. These antisera will be used to develop immunoassays to study vitellogenesis in mysids and to detect potential stimulatory or inhibitory effects of endocrine disruptors on the production of vitellin.     

Development of a quantitative enzyme-linked immunosorbent assay for vitellin in the mysid Neomysis integer (Crustacea: Mysidacea)

Mysid crustaceans have been put forward by several regulatory bodies as suitable test organisms to screen and test the potential effects of environmental endocrine disruptors. Despite the well-established use of mysid reproductive endpoints such as fecundity, egg development time, and time to first brood release in standard toxicity testing, little information exists on the hormonal regulation of these processes. Control of vitellogenesis is being studied intensively because yolk is an excellent model for studying mechanisms of hormonal control, and vitellogenesis can be chemically disrupted. Yolk protein or vitellin is a major source of nourishment during embryonic development of ovigorous egg-laying invertebrates. The accumulation of vitellin during oocyte development is vital for the production of viable offspring. In this context, we developed a competitive enzyme-linked immunosorbent assay (ELISA) for vitellin of the estuarine mysid Neomysis integer. Mysid vitellin was isolated using gel filtration, and the purified vitellin was used to raise polyclonal antibodies. The ELISA was sensitive within a working range of 4 to 500 ng vitellin/mL. Serial dilutions of whole body homogenates from female N. integer and the vitellin standard showed parallel binding curves, validating the specificity of the ELISA. The intra- and interassay coefficients of variation were 8.2% and 13.8%, respectively. Mysid vitellin concentrations were determined from ovigorous females and eggs at different developmental stages. The availability of a quantitative mysid vitellin ELISA should stimulate further studies on the basic biology of this process in mysids. Furthermore, it could provide a means to better understand and predict chemically induced reproductive effects in mysids.     

Phylogeography of an estuarine mysid, Neomysis integer (Crustacea, Mysida), along the north-east Atlantic coasts

Aim The brackish water mysid, Neomysis integer, is one of the most common mysid species along the coasts of the north‐east Atlantic. In the present study, the phylogeographical patterns were examined throughout the distribution range of N. integer. In particular, the latitudinal trends in genetic diversity and the distribution of genetic variation were examined in order to elucidate the imprints of the Pleistocene glaciations. Location North‐east Atlantic coasts from the Baltic Sea to the south of Spain. Methods A total of 461 specimens from 11 populations were analysed by means of single‐stranded conformation polymorphism analysis combined with DNA sequencing of a fragment of the mitochondrial cytochrome c oxidase I gene. The genetic structure was examined by using a progression of phylogenetic, demographic and population genetic analyses to elucidate not only the geographical structure, but also the evolutionary history producing that structure. Results The levels of genetic diversity were relatively uniform throughout the distribution range, with the exception of a decline at the northern and southern edges of distribution. A high heterogeneity was observed between the populations analysed (global Φ_ST = 0.787). This is caused by the disparate distribution of the cytochrome oxidase I haplotypes, with several population‐specific haplotypes. A clear genetic break (2.4% sequence divergence) occurred between the southernmost Guadalquivir population and all other populations. Main conclusions The present study corroborates the expectations of the genetic patterns typically observed in an estuarine species. The within‐population variability was low, whereas a significant (moderate to high) divergence was observed between populations. Phylogeographical analysis revealed that northern populations within the English Channel, North Sea and Baltic Sea are characterized by several widespread haplotypes, while the Irish population and all sites south of the Bay of Biscay consist solely of unique haplotypes. This pattern, combined with the relative high levels of genetic diversity, could be indicative for the presence of a glacial refugium in the English Channel region. Under this scenario N. integer must have survived the Last Glacial Maximum in the palaeoriver system present in that region.     

Comparative morphology and actuopalaeontology of mysid statoliths (Crustacea,Mysidacea)

Summary A comprehensive and comparative study of the external statolith morphology of the family Mysidae is presented. The study covers 48 species from major systematic groups occupying a large number of habitats in different biogeographical zones of the globe. Statoliths generally show high morphological diversity. The traditional classification scheme of subtaxa and the correlation of statolith characters with segmentation patterns of body appendages suggest that the organic composition and the nearly spherical structure of the statoliths of Boreomysinae and Rhopalophthalminae are plesiomorphic compared with the more complex mineralized statoliths found in all other subfamilies. During ontogenetic development the number of sensorial setae and associated pores and pore groups on the statolith increase with body size and statolith diameter. Although patterns of caudal pores are highly specific for some genera, the high intraspecific variance of pore numbers strongly reduces the diagnostic value of this feature in most species. Statolith characters can be successfully used for identification of subfamilies, tribes, and especially genera. For future palaeontological applications a proper diagnosis of fossil mysid statoliths is essential. Therefore, we provide a key to subfamilies and tribes based exclusively on statolith characters.     

Structure of recent and fossil mysid statoliths (Crustacea,Mysidacea)

Statoliths of 61 Recent species representing all subfamilies of Mysidae were studied with special emphasis on internal structure. In addition 5 samples of fossil statoliths from Miocene deposits were examined. Species of Boreomysinae and Rhopalophthalminae show simple roughly spherical organic statoliths, with setae originating from the sensory cushion and anchored in the statolith with distal branches extending shortly below the surface. All other subfamilies possess mineralized statoliths of greater structural complexity, with differentiation in core and mantle, where each part may consist of up to three layers. Habitus is hemispherical to discoidal. External gross structures are dorsal tegmen, ventral fundus, and the ambitus forming the outer toroidal to semi-toroidal circumference. Setae penetrate the mantle through mineralic canals and insert on the surface of the core. As suggested by congeneric species of Schistomysis, there is no principal structural difference between statoliths mineralized with fluorite compared to vaterite. However, vaterite statoliths tend to be more often of moruloid appearance and are exceptional by showing a central conical hole (the hilum) or a central cavity in certain forms. These structures are typical of fossil calcite statoliths. In vaterite and fluorite statoliths, the mantle shows radially arranged (= spherulitic) crystal aggregates. Such arrangements are badly preserved in fossil calcite statoliths. In large extant statoliths, concentric structures, mainly in the form of superficial striation and/or concentric microstrata, are visible in coexistence with radial aggregates. Stratification is possibly due to stratified deposition of the nonmineralized gland product, while the spherulitic structure is indicative of subsequent radial growth of crystal aggregates. The structure of accessory fluorite statoliths in the statocyst of Mesopodopsis slabberi leads to the hypothesis that mantle material is formed by secretions of the caudal statocyst gland. After demineralization of fluorite, vaterite and calcite statoliths, an organic template remains showing most essential morphological features of the statolith. From this we conclude that the structure of the statolith is (almost) entirely matrix mediated. © 1993 Wiley-Liss, Inc.     

Cellular energy allocation in the estuarine mysid shrimp Neomysis integer (Crustacea: Mysidacea) following tributyltin exposure

Recently, we described the cellular energy allocation (CEA) methodology to asses the effects of abiotic stress on the energy metabolism of the estuarine crustacean Neomysis integer (Crustacea: Mysidacea) [J. Exp. Mar. Biol. Ecol. 279 (2002) 61]. This short-term assay is based on the biochemical assessment of changes in the energy reserves (total carbohydrate, protein and lipid content) and the energy consumption (electron transport activity), and has been shown to be predictive of effects at the population level in daphnids [J. Aquat. Ecosyst. Stress Recovery 6 (1997) 43]. In the present study, the CEA methodology was evaluated using adult N. integer exposed for 96 h to the antifoulant tributyltinchloride (TBTCl). From a range-finding experiment with juvenile N. integer, a 96-h LC50 of 164 ng TBTCl/l was calculated. The energy metabolism of N. integer, as summarized by the CEA, was significantly altered by TBTCl exposure. Mysids exposed to 10, 100 and 1000 ng TBTCl/l consumed less energy and had lower respiration rates (in 10 and 1000 ng TBTCl/l treatments) than the control, resulting in a lower CEA. These changes at the cellular level occurred at environmentally relevant concentrations of the toxicant TBTCl which were an order of magnitude lower than reported effect concentrations for scope for growth in other marine invertebrates.     

Biogeographical division of antarctic and subantarctic by mysid (Crustacea: Mysidacea) fauna

Based on the distribution of 66 species of Mysidacea (Crustacea), a biogeographical analysis of the cold and temperate waters of the Southern Hemisphere was carried out. The expediency of separate division by pelagic and benthopelagic mysid faunas was supported. The original patterns of the division of Antarctic and subantarctic faunas are given. One biogeographical province and two subprovinces were distinguished by the fauna of pelagic mysids in the areas studied. Two biogeographical provinces and five subprovinces were distinguished by the fauna of benthopelagic mysids in the Antarctic and subantarctic.     

Doxomysis algoaensis, a new mysid species (Crustacea: Mysidacea) from Algoa Bay (South Africa)

Doxomysis algoaensis sp.nov. is described from Algoa Bay, South Africa where it is common in nearshore marine waters just beyond the breaker line. D. algoaensis sp.nov. is morphologically similar to D. australiensis, but can readily be distinguished by the shape and armature of the telson and the length of the exopod of the fourth male pleopod. The apical cleft is one fifth the telson length in the former species and one third the length in D. australiensis. The telson apex on each side of the cleft is also armed with five and four stout spines in the two species, respectively. In D. australiensis, the exopod of the fourth male pleopod is almost three times the length of the endopod; in D. algoaensis sp.nov., the exopod is only slightly longer than the endopod. Other distinctive features of D. algoaensis sp.nov. include the maxillary palp, which is only slightly broader than long and the greater number of spines on the endopod of the uropod.     

Assessment of the potential impact of the mysid shrimp, Neomysis mercedis, on Daphnia

Neomysis mercedis, an important invertebrate predator in somelakes and estuaries in North America, occurred at high densities(>2 mysids m^-3) in Lake Washington in the early 1960s, aperiod when Daphnia were scarce in the lake. Because Neomysisfeed selectively on Daphnia, it was hypothesized that mysidpredation contributed significantly to the scarcity of Daphnia.To evaluate this hypothesis, mysid abundance was monitored inthe lake (July 1989–February 1992), and whole lake predationimpacts on Daphnia were estimated. Mysid abundance varied from319 million, 0.1 mysids m^-3 (February 1992) to 4276 million,1.7 mysids m^-3 ( June 1991), and mysid biomass ranged from 1153(October 1991) to 4700 kg dry weight (November 1990). A peakin Daphnia consumption was noted during autumn, when total mysidbiomass was high. In late autumn/winter mysid consumption month^-1accounted for 28–95% of Daphnia biomass and 13–38%of production. Mysid densities in this study were 18x and 5xlower than in 1962 and 1975, respectively. By extrapolation,at a density of 3.5 mysids m^-3 observed in the early 1960s,total Neomysis consumption demand month^-1 exceeded 100% of Daphniabiomass (late autumn–early spring), and 100% of Daphniaproduction (late autumn–winter). Estimates of the totalmysid consumption demand in this study are thus in accord withthe hypothesis that Neomysis could control Daphnia abundancein Lake Washington.     

The effect of temperature on the post-embryonic growth of Neomysis intermedia Czernlawsky (Crustacea, Mysidacea) under laboratory conditions

The effect of temperature on post-embryonic growth of Neomysisintermedia was investigated under unlimited food conditionsin the laboratory. The effect of temperature on the size ofnewly released animals was negligibly small, but body size wasinversely related to temperature in adults. This was mainlycaused by the difference in the number of molts before maturation.The specific growth rate of N. intermedia increased exponentiallywith a temperature coefficient, Q₁₀ of 4.6 from 0.018 d^–13C to 0.21 d^–1 at 20C in juveniles, and with a temperaturecoefficient of 2.7 from 0.006 d^–1 at 3C to 0.05 d^–1at 25C in adults. The rate in juveniles levelled off above20C, and dropped at 29C. Brood size and brood interval decreasedwith temperature increase, while the daily specific reproductionrate increased. The specific growth rate of gravid females,including production of egg matter, increased exponentiallywith a temperature coefficient of 3.3 from 0.015 d^–1 at10C to 0.093 d^–1 at 25C. The present laboratory experiments confirmed the temperaturecontrol on the growth of N. intermedia suggested in a hyper-eutrophiclake.     

A new freshwater mysid from the Amazon, with a reassessment of Surinamysis Bowman (Crustacea: Mysidacea)

A new species of mysis, Surinamysis robertsonae , is described from the plankton of the Lago Calado, a whitewater lake in the Amazon Basin. This is only the second freshwater mysid to be described from the Amazon. Surinamysis Bowman, 1977, comprising S. robertsonae, S. americana and S. merista , is raised to full generic rank on the grounds of telson morphology (compared to the other species of the Antromysis group) and the flagelliform process of the male antennule.     

The biogeographical division of the Arctic and North Atlantic by the mysid (Crustacea: Mysidacea) fauna

The biogeographical analysis of Arctic and North Atlantic waters north of 30°N is based upon the distribution of 150 Mysidacea (Crustacea) species. The reasons for biogeographical divisions conducted independently by faunae of pelagic and benthopelagic mysids are adduced. The original schemes of the Arctic and North Atlantic division are proposed. Using the fauna of pelagic mysids, one biogeographical realm, one province and one transitional zone are designated in cold and temperate waters. Using the fauna of benthopelagic mysids, one biogeographical realm and four provinces are designated in those waters.     

Spelaeomysis cochinensis,a new mysid (Crustacea: Mysidacea) from a prawn culture field in Cochin,India

Spelaeomysis cochinensis sp. nov., the eighth species of the genus is described from a prawn culture field in Cochin, India. It is characterised by a pair of eye plates with few ommatidia and the fully spiny border of the telson.     

Fine Structure of the Organ of Bellonci (SPX) in Boreomysis arctica (Kroyer) (Crustacea, Mysidacea)

The organ of Bellonci (oB) in Boreomysis arctica (Krøyer) is described. The fine structure of the organ is found to agree with that of the oB among other investigated peracarideans. The difficulties met by Chaigneau in 1971 when homologizing the organs in B. arctica and in the Isopoda have been eliminated. Into the cavity of the oB, (probably) sensory neurones protrude. The perikarya of the neurones are found in the wall of the oB. On the dendrites there are subterminal dendritic swellings from which dendritic branches and cilia arise. The branching dendrites are characteristic of the oB in B. arctica. Also the cilia branch, thus increasing the amount of sensory membranes in the organ.     

Biology of the mysid Mesopodopsis slabberi (van Beneden, 1861) (Crustacea, Mysidacea) in a coastal lagoon of the Ebro delta (NW Mediterranean)

Aspects of the population and reproductive biologyof the mysid Mesopodopsis slabberi were studiedin the western Mediterranean (Encanyissada coastallagoon, Ebre delta, Spain). Misids were sampling atmonthly intervals from August 1993 to June 1995. InDecember 1994 and February 1995 any individuals werefound. The relationship between carapace length (Lc)and total length (Lt) was isometric:logLt = 1.0612logLc + 0.9411 (n = 178,r = 0.9411). Thesize of mature males and females was at a maximum inthe winter, and a minimum in the summer. The longevityof individuals changed throughout the year; those withthe longest life expectancy were members of theoverwintering generation. Brooding females wererecorded throughout the year, except in December 1993and April 1994; they were most numerous in spring andautumn. The number of embryos or larvae (N) carried byfemales was related to the size of the females (range:1–22, mean value: 4.8): logN = 1.8705logLc–0.0985(n = 361, r = 0.4097, P < 0.01). Thesize of the eggs(maximum diameter, Le) was related to the size of thefemales (range: 0.35–0.6 mm in total length):logLe = 0.3404logLc–0.4820 (n = 277, r = 0.5420, P < 0.01).